Unable to find "Subdivide Smooth" option in blender 2.8
The 'Subdivide Smooth' option in previous versions of Blender simply applied a Subdivide operation with the Smooth parameter set to 1.0 - the Smooth parameter is available in the Tool properties 'Redo' panel available in the left-hand panel.

It seems that in Blender 2.8 the menus have been pruned to remove unnecessary options - instead, you can adjust the 'Smoothness' by simply opening the tool properties (the floating Subdivide panel at the bottom-left) and varying Smoothness :



However, I don't think that is your complete solution - in your case, possibly you also need to set the mesh itself to 'Smooth' shading. At 2.8, this is available in the Object menu as 'Shade Smooth' :